The objective of this research is to elucidate the mechanisms of the primary action of polypeptide hormones on receptors in the surface membrane of responsive cells. The approach to this problem at present involves treatment of intact fat cells with reagents having specificity for the cell surface and then observing the consequences of such treatment on adenylate cyclase and other specific cell functions. Hormones under study include insulin, adrenocoritcotropin, glucagon and epinephrine. The studies have implications for insulin resistance in diabetes mellitus and for rates of fat cell proliferation and growth in various states of obesity.